Income Taxes Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Abstract]
Federal statutory tax rate	35.00%	35.00%	35.00%
Federal tax credits	(19.00%)	(11.40%)	(21.80%)
State and local taxes, net of federal tax benefit	4.20%	3.90%	3.40%
Flow through depreciation and cost basis differences	0.00%	(2.30%)	2.80%
Other	0.50%	0.80%	(2.60%)
Effective tax rate	20.70%	26.00%	16.80%